Interpretive Summary: Turkeys like other poultry face potential stressful situations including transfer between houses and some conditions which can cause leg problems. Sometimes, the birds are given supplemental vitamins and feed additives to counter the stress effects. To find whether these factors produce skeletal effects and protect against the effect of stress, we fed turkeys two feed supplements, vitamin D and yeast extract with or without simultaneously imposed artificial stress using a hormonal drug dexamethasone. We investigated their effect on growth and bone parameters. Although there were some beneficial effects of both supplements on normal birds, they could not protect against the effect of stress induced by dexamethasone.

Technical Abstract:
The effects of a yeast extract (YE) feed supplement and/or vitamin D3 (VD) on the bone properties of 16 wk-old turkeys, transiently subjected to a simulated stress using dexamethasone (Dex), were determined. The turkeys were fed diets with or without YE and/or VD during 6, 11, and 15 wk post hatch, respectively. At 6 wk of age, half of the birds in each treatment group were given intramuscular injections of Dex (2 mg/kg BW) on 3 alternating days to induce simulated stress. At 16 wk of age, the birds were weighed, bled before necropsy, and the tibia were harvested to determine bone properties. Bone mineral density (BMD), bone mineral content (BMC) were determined by dual energy X ray absorptiometry (DEXA), and the biomechanical strength by Instron material testing machine using whole bones. The bone density and the ash percentage, and the dry bone densities were determined using the bone marrow free mid diphyseal segments of contra lateral tibia. Serum Ca, P, and alkaline phosphatase changes in respective serum samples were also determined. Neither YE nor VD had any effect on BW by itself or in combination. The birds treated with Dex had lower BW and higher bone index compared with the control birds without Dex. Although no significant trends were observed in bone densities, the BMC of Dex treated birds were lower. Turkey poults fed VD supplemented diets with or without Dex treatment, showed increases in bone ash percentage and ash density. Only the normal control poults fed YE fed showed an increase in BMD and bone strength. Dex treatment lowered bone strength while increasing its stiffness. These results suggest that acute stress that affects the growth process can alter bone properties producing asynchronous changes in their physiology. Intermittent treatments with either VD or YE may not be sufficient to protect from the effects of severe stress.